1. Field of the Invention
This invention relates to thermal ink jet printing, and more particularly, to an improved method of fabricating a thermal ink jet printhead by a dicing operation capable of finishing the nozzle containing surface.
2. Description of the Prior Art
Thermal ink jet printing is a type of drop-on-demand ink jet systems, wherein an ink jet printhead expels ink droplets on demand by the selective application of a current pulse to a thermal energy generator, usually a resistor, located in capillary-filled, parallel ink channels a predetermined distance upstream from the channel nozzles or orifices. The channel end opposite the nozzles are in communication with a small ink reservoir to which a larger external ink supply is connected.
U.S. Pat. No. Re. 32,572 to Hawkins et al discloses a thermal ink jet printhead and several fabricating processes therefor. Each printhead is composed of two parts aligned and bonded together. One part is a substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes, and the second part is a substrate having at least one recess anisotropically etched therein to serve as an ink supply manifold when the two parts are bonded together. A linear array of parallel grooves are also formed in the second part, so that one end of the grooves communicate with the manifold recess and the other ends are open for use as ink droplet expelling nozzles. Many printheads can be made simultaneously by producing a plurality of sets of heating element arrays with their addressing electrodes on a silicon wafer and by placing alignment marks thereon at predetermined locations. A corresponding plurality of sets of channel grooves and associated manifolds are produced in a second silicon wafer. In one embodiment, alignment openings are etched in the second silicon wafer at predetermined locations. The two wafers are aligned via the alignment openings and alignment marks, then bonded together an diced into many separate printheads.
U.S. Pat. No. 4,638,337 to Torpey et al discloses an improved thermal ink jet printhead similar to that of Hawkins et al, but has each of its heating elements located in a recess. The recess walls containing the heating elements prevent the lateral movement of the bubbles through the nozzle and therefore the sudden release of vaporized ink to the atmosphere, known as blow-out, which causes ingestion of air and interrupts the printhead operation whenever this event occurs. In this patent a thick film organic structure such as Riston.RTM. or Vacrel.RTM. is interposed between the heater plate and the channel plate. The purpose of this layer is to have recesses formed therein directly above the heating elements to contain the bubble which is formed over the heating elements, thus enabling an increase in the droplet velocity without the occurrence of vapor blow-out and concomitant air ingestion.
U.S. Pat. No. 4,097,310 to Lindmayer discloses a method of forming silicon solar cells by forming an electron generating junction on a single crystal wafer followed by a diamond blade cut through the wafer. Rotation speeds for the diamond blade fall into the range of 5,000 to 20,000 rpm with a corresponding cutting speed of 0.05 to 10 inches per second.
U.S. Pat. No. 4,564,000 to Stern et al discloses a method of cutting ferrite materials using a resin bonded diamond sawblade at a cutting speed of 5400 centimeters per second. The blade itself has a diameter of 2.25 inches. Cooling means are applied to the blade to prevent overheating of the blade and the ferrite.
U.S. Pat. No. 4,633,847 to Lossl et al discloses a multiple-blade internal hole sawing method for cutting crystal-line rods into thin wafers while maintaining a connection between adjacent cut wafers. The wafers can be cut into thicknesses ranging from 0.1mm to 1.0mm. Connecting agents, such as wax, are used to mechanically connect the cut wafers but can easily be removed by solvent or heating.
Japanese Patent Application No. 59-10182, filed in Japan on Jan. 25, 1984, and published without examination on Aug. 14, 1985, as Laid-Open No. 60-154639 to Mimata discloses a method and apparatus for dicing wafers using rotary blades of different widths to cut grooves into the wafers. The cut with a first rotary saw is deep enough to remove patterns but the through-wafer dicing is done by another rotary saw of a smaller width.
In all ink jet printing systems, the nozzle or orifice size, shape, and surface conditions affect the characteristics and trajectory of the ink droplet emitted from the nozzle. Some ink jet printers have a separate nozzle plate which is independently fabricated to obtain the desired dimensional tolerances and surface conditions. This nozzle plate is then aligned and bonded to the droplet generator or printhead. In addition to the dimensional precision, attachment is sometimes difficult and debonding is a constant concern. Also, if an adhesive is used, it may flow into the nozzle or ink paths, thereby restricting or impairing the droplet ejection and/or trajectory. Other ink jet printers have printheads fabricated from two substrates, as disclosed in the prior art discussed above, in which one substrate contains the heating elements and the other contains ink recesses, which, when the substrates are aligned and bonded together, serve as ink passageways. The open ends of the passageways terminate about 1.0 to 5.0 mils in front of the heating elements and create the nozzles. The front face of the printhead containing the nozzles have a major impact on the droplet characteristics and trajectories. One discontinuity at the nozzle is made by the adhesive bond and has a tendency to cause weeping of the ink therefrom. Generally, a polishing operation removes the bonding discontinuity as well as other surface defects.
In these and other fabrication methods, the printhead nozzle plate with nozzle containing surface must be fabricated separately and bonded to the printheads, photolithographically produced separately by complex photo-processing, or the nozzle containing surface must be polished. All of these methods of fabrication do not lend themselves well to making economical or technically sound devices.
This invention overcomes the disadvantages of the prior art fabrication methods and enables an acceptable nozzle and nozzle containing surface finish to be concurrently formed in one process step. Use of an optimized dicing blade and dicing process with predetermined operating parameters, enable the concurrent sectioning of the mated wafers into individual printheads and forming of the nozzle containing surface. This surface has a finish sufficient to prevent deleterious effect on the droplet or its trajectory without the need of further processing.